This disclosure relates to systems and methods for converting full color images to highlight color.
A significant amount of color printing can be performed using a highlight color printer. In this type of printing, only two inks are used in the printing process. These inks comprise black and a highlight color (usually red or blue). Electronic printers may be designed specifically for highlight color painting. Highlight color printers are generally faster and less expensive than full color printers because only two inks are processed, as opposed to the three or four inks, which must be processed in order to obtain full color images. One such application is a teacher's edition textbook, which includes single color main text, such as black, and highlight color answers, printed in a highlight color such as red.
Images and text specifically created for highlight printing can typically be reproduced accurately. However, images created for other printer systems, such as full color printers, or highlight color images scanned or mapped into a 3-D color space, such as RGB, may not print with desirable results because the gamut of all of the image colors, shades, tints and hues cannot be faithfully reproduced by the highlight printer. Additionally, once mapped into a multi-bit, 3-D color space, such as RGB, processing becomes lengthy because of the large amount of data needed to represent the image. For example, what was once simple, two color image data is scanned into multi-bit image data.
The gamut of full colors is a three-dimensional volume that can be represented by a double hexagonal cone. In this representation, shades vary from dark to light as one moves upwards vertically. Tints vary from unsaturated grays to fully saturated colors as one moves out radially. Hues vary as one moves angularly in the horizontal plane.
The gamut of colors available to a highlight printer can be represented by the two-dimensional triangle. This is a slice from the fall color double hexagonal cone at the angle of the highlight hue.
Prior attempts to print a full color image on a highlight color printer typically involved specific mapping of the three-dimensional double hexagonal cone to the two-dimensional triangle. Examples of such conversions can be found in U.S. Pat. No. 6,115,493 to Harrington, U.S. Pat. No. 6,185,013 to Harrington et al., U.S. Pat. No. 6,721,069 to Harrington, U.S. Pat. No. 5,237,517 to Harrington et al., and U.S. Pat. No. 6,426,802 to Lin, the disclosures of which are hereby incorporated herein by reference in their entireties. In such systems, the printer makes its best effort to render the highlight color image by mapping the full color specification into the set of colors that it clan produce. In such a mapping, many different colors in the full color space will be mapped to the same color in the highlight color space.